Veterinary Society of
Surgical Oncology


General Considerations

  • ovarian tumors are uncommon in cats and dogs
  • ovarian tumors account for 0.7%-3.6% of all tumors in cats and 0.5%-1.2% of tumors in dogs
  • ovarian tumors are more common in older nulliparous bitches
  • granulosa-theca cell tumor and Sertoli-Leydig cell tumor are the most common ovarian tumors


General Considerations

  • epithelial tumors account for 40%-50% of all ovarian tumors in dogs, but are very rare in cats
  • breed predisposition: Pointers
  • types: papillary adenoma, papillary ADC, cystadenoma, and undifferentiated carcinoma
  • metastasis of LSA and endometrial ADC to the ovaries has been reported in cats

Papillary Adenoma and Adenocarcinoma

  • papillary adenoma and ADC can be bilateral
  • differentiation between papillary adenoma and ADC is difficult and based on size, mitotic index, invasion into ovarian stroma, and extension into ovarian bursa and adjacent peritoneum
  • papillary ADC associated with widespread peritoneal implantation and malignant effusion
  • malignant effusion develops due to:
  • edema within the ovarian tumor resulting in fluid leakage the through tumor capsule
  • exfoliation and implantation of tumor cells resulting in occlusion of peritoneal and diaphragmatic lymphatics
  • secretions from metastatic peritoneal implants
  • 50% metastatic rate with metastasis to the renal and para-aortic lymph nodes, omentum, liver, and lungs


  • cystadenoma originates from rete ovarii
  • unilateral
  • multiple thin-walled cysts containing clear serous fluid

Undifferentiated Carcinoma

  • embryonal morphology and absence of hormonal secretion
  • 50% metastatic rate


General Considerations

  • germ cell tumors account for 6%-20% of all canine ovarian tumors
  • types: dysgerminoma, teratocarcinoma, and teratoma


  • dysgerminoma arise from undifferentiated germ cells and consist of a uniform population of cells resembling primordial ovarian germ cells
  • dysgerminoma resembles testicular seminoma in male dogs and have been termed ovarian seminoma
  • dysgerminoma represents 15% of all feline ovarian tumors
  • dysgerminomas are usually unilateral, but bilateral tumors have been reported (especially in cats)
  • dysgerminoma grow by expansion rather than invasion
  • 10%-30% metastatic rate with metastatic sites including abdominal lymph nodes (common), liver, kidney, omentum, pancreas, adrenal glands, and brain


  • teratomas are more common in bitches < 6 years
  • teratoma is composed of ≥ 2 germinal cell layers with any combination of ectodermal, mesodermal, and endodermal tissue
  • teratomas are usually well-differentiated


  • teratocarcinomas consists of mature and undifferentiated elements
  • 32%-50% metastatic rate with metastasis to multiple abdominal sites, lungs, cranial mediastinum, and bone
  • metastatic lesions composed primarily of undifferentiated tissue


General Considerations

  • sex-cord stromal tumors account for 34%-50% of ovarian tumors in cats and dogs
  • types: granulosa cell tumor (common), thecoma, and luteoma
  • sex-cord stromal tumors are unilateral although Sertoli-Leydig cell tumors are bilateral in 36% dogs
  • sex-cord stromal tumors are functional tumors as they arise from specialized gonadal stroma of the ovary which is responsible for the production of estrogen and progesterone

Granulosa Cell Tumor

  • breed predisposition: English Bulldog
  • gross appearance: firm and lobulated
  • Call-Exener body formation is diagnostic with gland-like or rosette patterns of abortive follicle formation often containing a central secretory globule which resembles an ovum
  • > 50% metastatic rate in cats with metastasis to the peritoneum, sublumbar lymph nodes, omentum, diaphragm, kidney, spleen, liver, and lungs
  • 20% metastatic rate in dogs with metastasis to the sublumbar lymph nodes, liver, pancreas, lung, and peritoneal carcinomatosis

Thecoma and Luteoma

  • thecomas and luteomas are rare
  • luteoma occurs more commonly in cats than dogs
  • thecoma is histologically similar to FSA and differentiated from FSA due to presence of lipid droplets
  • thecomas are benign with expansile growth rather than invasion
  • thecomas can be functional with production of estrogen more common than testosterone

Tumor-Like Conditions

  • ovarian cysts can be very large
  • paraovarian cysts arise from mesonephric ducts and can either be single or multiple
  • other: cystic rete tubules, vascular hematoma, and adenomatous hyperplasia of rete ovarii


Clinical Signs

  • young dogs commonly affected with teratomas and middle-aged to older animals with other ovarian tumors
  • space-occupying mass is the most common sign
  • epithelial tumors can produce malignant effusion with characteristic signet ring and rosette cellular pattern
  • sex-cord stromal tumors are functional:
  • excessive estrogen production results in vulvar enlargement, hyperplasia and cornification of vaginal epithelium, sanguineous vulvar discharge, persistent estrous, alopecia, and aplastic pancytopenia
  • excessive progesterone production results in cystic endometrial hyperplasia and pyometra
  • thecomas are associated with feminizing effects and luteoma with masculinizing effects, but both are rare
  • dysgerminoma in cats associated with depression, vomiting, abdominal distension, and ascites


  • abdominal mass ± clinical signs referable to the reproductive tract
  • survey radiographs: calcification with teratoma
  • excretory urography can be used to differentiated renal and ovarian tumors
  • thoracic radiographs for metastatic disease but rarely positive at the time of diagnosis
  • benign lesions usually appear cystic with well-defined margins on abdominal ultrasonographic examination, whereas malignancy is more likely when ovarian masses have a proportion of the mass appearing solid
  • aspiration is not recommended due to propensity for exfoliation and implantation on peritoneal surface
  • histopathology


Medical Management

  • intracavitary cisplatin for management of malignant effusion
  • platinum drugs with tamoxifen used in metastatic human ovarian tumors
  • hectate-b significantly decreases tumor burden

Surgical Management

  • ovariohysterectomy or ovariectomy
  • gentle handling is required to minimize tumor exfoliation and peritoneal seeding


  • prognosis is good if single tumor with complete excision and no evidence of metastatic disease
  • survival time of up to 4 years for dysgerminoma and 6 years for teratoma have been reported
  • chemotherapy has the potential to prolong life in animals with metastatic ovarian tumors


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